WO2012125916A2

WO2012125916A2 - Heated under-body warming system

Info

Publication number: WO2012125916A2
Application number: PCT/US2012/029414
Authority: WO
Inventors: Scott D. Augustine; Ryan S. Augustine; Randall C. Arnold; Rudolf A. Deibel; Scott A. Entenman; Thomas F. Neils; Keith J. Leland
Original assignee: Augustine Temperature Management, Llc
Priority date: 2011-03-16
Filing date: 2012-03-16
Publication date: 2012-09-20
Also published as: EP2685954A4; US20120279953A1; WO2012125916A3; EP2685954A2

Abstract

A heated underbody support comprising a heated mattress, heated mattress overlay or heated pad. The heated underbody support includes a heater assembly having an upper surface upon which a user directly or indirectly lays when the heated underbody support is in use. The heater assembly includes a flexible heating element including a sheet of conductive fabric having a substantially uniform Watt density. The heated underbody support also includes a layer of compressible material adapted to conform to the user's body when under pressure from the user resting upon the support. When the user lays upon the upper surface of the support, the heating element is adapted to adjust such that the temperature of the contact portion is less than the temperature of the non-contact portion of the support.

Description

HEATED UNDER-BODY WARMING SYSTEM

BACKGROUND

There have been many attempts at making heated mattresses and heated mattress overlays for therapeutic patient warming. Therapeutic patient warming is especially important for patients during surgery. It is well known that without therapeutic intraoperative warming, most anesthetized surgical patients will become clinically

hypothermic during surgery. Hypothermia has been linked to increased wound infections, increased blood loss, increased cardiac morbidity, prolonged ICU time, prolonged hospital stays, increased cost of surgery and increased death rates.

Since the early 1990s, the standard of care for surgical warming has been forced air warming blankets. Prior to that time, warm water mattresses were commonly used. The warm water mattresses went out of common use because they were relatively stiff and inflexible. The stiff water mattress negated any pressure relief that the under-laying support mattress may have provided. As a result, the combination of pressure applied to the bony prominences and the heat from the warm water mattress both reduced blood flow and accelerated metabolism, causing accelerated ischemic pressure injuries to the skin ("bed sores"). Additionally, the warmed water recirculating in the warming system could become contaminated with bacteria, which was especially important when a leak occurred. As a result, warm water mattresses are rarely used today.

Historically, electrically heated pads and blankets for the consumer market have been made with resistive wire heaters. The safety of wire- based heaters has been questionable in consumer applications. However, in the operating room environment with anesthetized patients, the possibility of hot spots caused by the wires in normal use and the failure mode of broken heater wires resulting in sparking, arcing and fires are unacceptable. Therefore, resistive wire-based heaters are rarely used in the operating room today.

Since the mid 1990s, unsuccessful attempts have been made to make effective and safe heated mattresses for operating room use using flexible, sheet-like electric resistance heaters. Sheet-like heaters have been shown to be more effective in warming patients because of the even heat production and generally they do not cause arcing and sparking when they fail.

Sheet-like heaters found in some existing devices use a carbon-filled electrically conductive plastic ink, printed on and laminated between two sheets of polyester film. The resulting heater and bus bar assembly is relatively stiff, non-conforming and non- stretching.

In other devices, the heater material is a carbon impregnated plastic film. The film may contain greater than 50% carbon by weight. The carbon-laden plastic film is relatively weak and non-elastic and therefore may be extruded or laminated onto a woven fabric for stability and to prevent tearing. Metal film or woven wire bus bars can be bonded to the conductive plastic with a conductive adhesive and then potted in a thick layer of plastic or laminated between sheets of plastic for durability and strength. Such fabric-reinforced film heaters can be relatively flexible, but are not stretchable or elastic. The bus bars are relatively stiff and inflexible and totally non-stretchable.

Electrically conductive fabric made of carbon fibers has been used as heater material in therapeutic blankets. However, carbon fiber fabric has not been used for therapeutic mattresses. Carbon fiber fabric used in heating elements are stabilized by laminating it between layers of plastic film in order to keep the "slippery" fiber bundles from shifting randomly and altering the electrical conductivity and heat production.

Additionally, the carbon fibers can fracture over time with repeated flexing, which also changes the electrical conductivity. Fiber fracturing can be minimized by laminating the fabric between layers of plastic film. The stiffer the resultant laminate, the more protective it is of the fibers.

Clearly, there is a need for conductive fabric heaters for use in therapeutic heated mattresses that are highly flexible, stretchable in at least one direction and durable without needing lamination to stabilize or protect the heater fabric. There is also a need for bus bar construction that does not result in thick, stiff, inflexible areas along the side edges of the heater. Then, maximally effective and safe therapeutic heated mattresses need to be designed using the stretchable, durable fabric heaters. SUMMARY

Various embodiments include flexible and conformable heated underbody supports including mattresses, mattress overlays, and pads for providing therapeutic warming to a person, such as to a patient in an operating room setting. In various embodiments, the heated underbody support is maximally flexible and conformable allowing the heated surface to deform and accommodate the person without reducing the accommodation ability of any under-laying mattress, for example.

The heated underbody support may include a heater assembly including an upper surface upon which a user directly or indirectly lays when the heated underbody support is in use. The heater assembly may include a flexible heating element including a sheet of conductive fabric having a top surface, a bottom surface, a first edge and an opposing second edge, a length, and a width and may have a substantially uniform Watt density. The heater assembly may also include a first bus bar extending along the first edge of the heating element and adapted to receive a supply of electrical power, a second bus bar extending along a second edge of the heating element, and a temperature sensor. The heated underbody support may also include a layer of compressible material adapted to conform to the user's body when under pressure from the user resting upon the support. When the user lays upon the upper surface of the support, the area of contact between the user and the upper surface of the support may define a contact portion of the support separate from a non-contact portion of the support, with the temperature sensor being located within the contact portion of the support. The heating element may be adapted to adjust such that the temperature of the contact portion is less than the temperature of the non-contact portion of the support.

In some embodiments, the support also includes a controller adapted to regulate the supply of electrical power to the first bus bar depending upon input from the temperature sensor so as to maintain a desired temperature. When the user is positioned on the contact portion and on the temperature sensor, the controller may maintain the temperature of the contact portion at the desired temperature which is less than the temperature of the noncontact portion of the support.

In some embodiments, the sheet of conductive fabric comprises a fabric coated with an electrically conductive or semi-conductive material such as a carbon fiber or metal containing polymer or ink or a polymer such as polypyrrole. The conductive fabric may include thread separately and individually coated with the conductive or semi- conductive material such that the coated threads of the fabric are able to slide relative to each other such that the heating element is stretchable. In some embodiments, the heating element has a generally planar shape and, in response to pressure, the heating element is adapted to stretch into a 3-dimensional compound curve without wrinkling or folding while maintain electrical conductivity and is further adapted to return to the generally planar shape when pressure is removed. In some embodiments, the heating element has a first Watt density when in a generally planar shape and a second Watt density when stretched into a 3 dimensional compound curve, with the first Watt density being greater than the second Watt density.

In some embodiments, the layer of compressible material is a layer of foam having a top surface and a bottom surface and the heating element is located on the top surface of the layer of foam. The layer of foam may be contoured such that either the top surface and/or the bottom surface is not planar over the entire surface. The first and second edges of the foam layer may be angled inwardly toward the top surface. In some embodiments, the bottom surface of the layer of foam is nonplanar and includes one or more channels extending substantially across the entire length or width of the layer of foam. In some embodiments, the channel or channels are located at a position that aligns with a line of flexion of a table or mattress with which the underbody support is designed to be used. In some embodiments, the channel or channels are located at a position that aligns with a longitudinal line of flexion allowing the support to flex around a longitudinal axis of the user when the user is laying on the heated underbody support in a lateral position. In some embodiments, the foam layer includes a central area having a reduced thickness relative to a thickness of a peripheral area of the foam layer. In some embodiments, the top surface of the foam layer includes a half-pipe or half-cylinder shaped depression in a central area to accommodate, partially surround and accurately position a pediatric patient. In some embodiments, the foam layer includes a central area and a peripheral area, and the foam material of the central area is less dense than the foam of the peripheral area. In some embodiments, the heated underbody support also includes a water resistant shell encasing the heater assembly and the layer of compressible material which may include an upper shell and a lower shell which are sealed together along their edges to form a bonded edge.

In some embodiments, the first and second conductive bus bars are attached to the heating element by sewing through the bus bar and the heating element with electrically conductive thread. In some embodiments, a strip of electrically insulating fabric or film is interposed between the heating element and the bus bar, and the bus bar is electrically connected to the heating element by sewing through the bus bar and the electrically insulating fabric or film and the heating element with electrically conductive thread.

The temperature sensor may be located in contact with the heating element. In some embodiments, a thin layer of foam is positioned over the temperature sensor on the top surface of the heating element. In some embodiments, a thin ring of foam is positioned around the temperature sensor on the top surface of the heating element.

The compressible material may include one or more inflatable chambers such as flexible air filled chambers. The flexible air filled chambers may be elongated and have a longitudinal axis and may be positioned with their longitudinal axis parallel to each other, along side one another, extending substantially from a first side of the heated underbody support to an opposing second side if the heated underbody support. The flexible air filled chambers may each be capable of being inflated and deflated independently while the heated underbody support is in use. The flexible air filled chambers may be all capable of being inflated and deflated simultaneously while the heated underbody support is in use. In some embodiments, the flexible air filed chambers can be inflated and deflated in groups including less than all of the flexible air filled chambers, while the heated underbody support is in use. In some embodiments, the flexible air filled chambers are elongated and positioned side by side and are in alternating groups such that each flexible air filled chamber is in a different group from each flexible air filled chamber which is beside it.

In some embodiments, the heated underbody support includes air conduits, with one air conduit in independent fluid communication with each group of flexible air filled chambers for independently introducing or removing air from that group of flexible air filled chambers. In some embodiments, the heated underbody support also includes a pressure sensor adapted to detect an actual internal air pressure of the flexible air filled chambers, and a controller including a comparator for comparing a desired internal air pressure of the flexible air chambers with the actual internal air pressure. The controller may also include a pressure compensator for adjusting the actual internal pressure and may be in operative connection with the air conduits and an air pump. The controller may be adapted to adjust the inflation of the groups of flexible air chambers to maintain the desired internal air pressure of the flexible air filled chambers using data derived from the comparator.

In some embodiments, each flexible air filled chamber of each group of chambers is in fluid connection with every other flexible air filled chamber of its group so that each flexible air filled chamber reacts to air pressure changes in every other flexible air filled chamber of its group, thereby redistributing changes in air pressure within each flexible air filled chamber of each group. An interface pressure may be maintained on a top surface of each of the group of flexible air filled chambers which is engaged with or in contact with a portion of the user's body at an average pressure below a capillary occlusion pressure threshold of 32 mm Hg.

In some embodiments, the heated underbody support includes a heater assembly having an upper surface upon which a user rests during use of the support. The heater assembly may include a flexible heating element including a sheet of conductive fabric having a top surface, a bottom surface, a first edge and an opposing second edge, a length, and a width, a temperature sensor, and a controller that regulates a supply of power to the flexible heating element depending upon input from the temperature sensor to maintain a desired temperature. The flexible heating element may have a generally planar shape and an approximately uniform Watt density and, when the user contacts a portion of the heating element, the heating element may be adapted to automatically decrease in temperature in the portion. In some embodiments, when the user lays upon a portion of the upper surface of the support, the area of contact between the person and the support defines a contact portion of the support separate from a non-contact portion of the support, and the heating element is adapted to adjust a temperature of the contact portion to be less than a temperature of the non-contact portion. In some embodiments, the temperature sensor is centrally located on the heating element at a location upon which the user is typically positioned during normal use. In some embodiments, when the support is in use with the user on the contact portion, the controller maintains the temperature in the contact portion at the desired temperature which is less than the temperature of the non-contact portion.

Embodiments further include methods of warming a person using any of the heated underbody supports described herein. The methods include positioning the person on the upper surface of a heated underbody support, activating the heated underbody support to supply power to the heating element, and directing the underbody support to maintain a desired temperature, though not necessarily in that order. The location of the person on the support may define a contact portion of the support separate from a non- contact portion of the support, and a temperature of the contact portion may be less than a temperature of the non-contact portion. In some embodiments, the temperature sensor is centrally located on the heating element and positioning the person includes positioning the person to be in contact with the temperature sensor or with a portion of the support which overlies the temperature sensor. In some embodiments, the method also includes repositioning the person on the upper surface of the support such that part of the non- contact portion becomes an additional part of the contact portion of the support, and the temperature of the additional part of the contact portion automatically reduces to the desired temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings are illustrative of particular embodiments and therefore do not limit the scope of the invention. The drawings are not to scale (unless so stated) and are intended for use in conjunction with the explanations in the following detailed description. Various embodiments will hereinafter be described in conjunction with the appended drawings, wherein like numerals denote like elements.

FIG. 1 is a cross sectional view of a heater assembly undergoing deformation in accordance with some embodiments.

FIG. 2 is a cross sectional view of a heater assembly in accordance with some embodiments. FIG. 3 is an illustration of a heater assembly in accordance with some embodiments.

FIG. 4 is a cross sectional view of a heated mattress overlay or pad in accordance with some embodiments.

FIG. 5 is a cross sectional view of a heated mattress overlay or pad in accordance with some embodiments.

FIG. 6 is a cross sectional view of a heated mattress overlay or pad in accordance with some embodiments.

FIG. 7 is an illustration of a heated mattress overlay or pad in accordance with some embodiments.

FIG. 8 is a cross sectional view of a heated mattress overlay or pad in accordance with some embodiments.

FIG. 9 is a cross sectional view of a heated mattress overlay or pad in accordance with some embodiments.

FIG. 10 is a cross sectional view of a heated mattress overlay or pad in accordance with some embodiments.

FIG. 11 is a cross sectional view of a heated mattress overlay or pad with partial thickness cuts or channels in the foam layer in accordance with some embodiments.

FIG. 12 is an illustration of a heated mattress overlay or pad with a segmented foam layer in accordance with some embodiments.

FIG. 13 is a cross sectional view of a heated mattress overlay or pad with a contoured foam layer in accordance with some embodiments.

FIG. 14 is an illustration of a heated mattress overlay or pad with a foam ring by the temperature sensor assembly in accordance with some embodiments.

FIG. 15 is a cross sectional view of a heated mattress overlay or pad with a foam ring surrounding the temperature sensor assembly in accordance with some

embodiments.

FIG. 16 is a cross sectional view of a heated mattress including a visco-elastic foam layer in accordance with some embodiments.

FIG. 17 is a cross sectional view of a heated mattress including an inflatable chamber in accordance with some embodiments. FIG. 18 is a cross sectional view of a heated mattress including plurality of inflatable chambers in accordance with some embodiments.

FIG. 19 is a cross sectional view of a heated mattress including a plurality of inflatable chambers in accordance with some embodiments.

FIG. 20 is a schematic diagram of a console in accordance with some

embodiments.

DETAILED DESCRIPTION

The following detailed description is exemplary in nature and is not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the following description provides practical illustrations for implementing exemplary embodiments of the present invention. Examples of constructions, materials, dimensions, and manufacturing processes are provided for selected elements, and all other elements employ that which is known to those of skill in the field. Those skilled in the art will recognize that many of the examples provided have suitable alternatives that can be utilized.

Embodiments include heated underbody supports which include heated mattresses, heated mattress overlays, and heated pads. The term underbody support may be considered to encompass any surface situated below and in contact with a user in a generally recumbent position, such as a patient who may be undergoing surgery, including heated mattresses, heated mattress overlays and heated pads. Heated mattress overlay embodiments may be identical to heated pad embodiments, with the only difference being whether or not they are used on top of a mattress. Furthermore, the difference between heated pad embodiments and heated mattress embodiments may be the amount of support and accommodation they provide, and some pads may be insufficiently supportive to be used alone like a mattress. As such, the various aspects which are described herein apply to mattresses, mattress overlay and pad embodiments, even if only one type of support is shown in the specific example.

Various embodiments provide patient warming effectiveness by increasing accommodation of the patient into the heated mattress, mattress overlay, or pad, in other words, by increasing the contact area between the patient's skin and the heated surface of the mattress or mattress overlay. The heating element, and the foam or air bladders of the mattress, which may also be included, are easily deformable to allow the patient to sink into the mattress, mattress overlay, or pad. This accommodation increases the area of the patient's skin surface in contact with the heated mattress, mattress overlay, or pad and minimizes the pressure applied to the patient at any given point. It also increases the surface contact area for heat transfer and maximizes blood flow to the skin in contact with the heat for optimal heat transfer. The accommodation of the patient into the mattress, mattress overlay, or pad is not hindered by a stiff, non-conforming, non- stretching, hammocking heater. Additionally, in various embodiments, the heating element is at or near the top surface of the underbody support, in thermally conductive contact with the patient's skin, not located beneath thick layers of foam or fibrous insulation.

In certain embodiments, the heater assembly includes a heating element made of a conductive material. The conductive material may be stretchable in at least one direction or, alternatively, in at least two directions. One way to create a stretchable fabric heating element is to coat a conductive material onto individual threads or fibers of a carrier fabric. The threads or fibers may be woven or knitted, for example, into a stretchable fabric. Other examples of conductive fabrics which may be employed by some embodiments include, without limitation, carbon fiber fabrics, fabrics made from carbonized fibers, and woven or non-woven substrates coated with a conductive material, for example, polypyrrole, carbonized ink, or metalized ink.

The conductive material may be applied to the fibers or threads before they are woven or knit into a fabric. In this way, the coated threads can move and slide relative to each other as the fabric is stretched, and can return to their original orientation when the stretching is stopped such that the fabric can return to its original shape. Alternatively, the conductive materials that coat the individual fibers in the fabric may be applied after the fabric is woven or knit using a dipping, spraying, coating or polymerization process or combinations thereof. A conductive polymer can be selected that coats to the individual threads without bonding them together such that the threads remain able to slide relative to each other. Types of materials which may be used for the fabric base include natural and synthetic materials such as polyurethane-polyurea copolymer (for example spandex or Lycra made by INVISTA, Wichita, KS, polyester, polyamide, (for example Nylon) or combinations thereof. The material may be elastic in nature such that the threads or fibers can stretch and then return to their original size or length. Alternatively or additionally, stretch and elasticity may be provided by the manner in which the threads or fibers are knit or woven, such as by forming a twill weave. Alternatively or additionally, stretch and elasticity may be provided by the manner in which fibers or groups of fibers are twisted or combined prior to being knit or woven into fabric. Alternatively, or additionally, the stretch and elasticity may be provided by the structure introduced to the fabric through shaping of the physical structure or shape of the fabric such as by embossing, creping or other mechanical means. Alternatively or additionally stretch and elasticity may be provided by the use of stretchable polymer or fibers in a nonwoven fabric.

The conductive coating may be applied to the individual fibers or threads before or after forming a fabric by spraying, coating or dipping, for example. Various conductive materials may be used. Examples include conductive and semi-conductive polymers include polypyrrole, polyaniline and polyacetylene.

In some embodiments, in contrast to some non-stretchable conductive film heaters where a carbon (or other conductive material) impregnated plastic film is extruded onto or bonded onto a base layer such as a fabric base layer, the heating element material may have a conductive or semi-conductive material coated onto the individual threads or fibers of the carrier fabric. This maintains the natural flexibility and stretch-ability of the fabric rather than turning the fabric into a non-stretchable fiber reinforced film.

In some embodiments, the conductive or semi-conductive coating may comprise a polymer and is bound as a layer surrounding the individual threads or fibers by a process of polymerization. Polymerization results in a very secure bond. The flexible coating on each individual thread or fiber may not crack, fracture or delaminate during flexion. Polymerization of these conductive or semi-conductive materials onto individual fibers of the carrier fabric is one example of a process for producing a durable, flexible and stretchable heater assembly according to some embodiments. Semi-conductive polymer coatings such as polypyrrole may be used in some embodiments, however, other coating processes are anticipated and conductive coatings that use carbon or metal as the conductive material are also anticipated.

The electrically conductive or semi-conductive fabric heater materials used in heating elements may be highly flexible and durable such that neither the carrier fiber nor the semi-conductive polymer coating will fracture with repeated flexing, loading and stretching. Additionally, the conductive or semi-conductive fabric heating element of various embodiments does not require lamination between layers of plastic film for protection or stabilization, though it may be laminated if desired.

The heating element comprises a flexible flat sheet of the conductive material. In some embodiments, it is rectangular having opposing first and second edges and opposing third and fourth edges extending from the first to second ends, a first planar surface and an opposing bottom planar surface. According to some embodiments, the heating element also includes closely spaced conductive elements such that the heating element has a substantially uniform Watt density output, in some embodiments less than approximately 0.5 watts/sq. inch, such as between approximately 0.1 and approximately 0.4 watts/sq. inch, of one or both surfaces, across a portion of or the entirety of the surface including and extending to the edges of the heating element. The closely spaced elements can be conductive threads woven into the fabric or conductive materials such as conductive ink applied to the fabric.

According to an exemplary embodiment, a conductive fabric comprising the heating element comprises woven polyester fibers individually coated with polypyrrole (available from Eeonyx Inc., Pinole, CA).

The stretchable fabric heating element is able to deform in response to a focal pressure applied to the surface of the heater fabric, into a smooth 3-dimensional compound curve without wrinkling or folding. A smooth compound curve cannot be formed out of non-stretchable fabrics or films. The stretchable fabric heating element may also exhibit elastic properties that allow it to revert to its original planar shape when the deforming pressure is relieved.

An example of a heater assembly 1 including a stretchable fabric heating element

10 is shown in Figure 1 , which depicts a cross section of a portion of the heater assembly 1. This example includes a heating element 10, a compressible material layer 20 beneath the heating element 10 and bonded to the heating element 10 by a layer of adhesive 30. The heater assembly 1 also includes an upper shell 40 and a lower shell 42. The heater assembly 1 curves smoothly under pressure from a patient's body (not shown) to stretch into an area of compound curve deformation 22.

In the embodiment shown in Figure 1 and in several other embodiments, a compressible material layer 20 is included beneath the heating elements 10. However, the compressible material layer 20 may alternatively be described as a layer of foam in each of these embodiments but is not limited to foam. For example, the layer of compressible material may comprise gel, stuffing material such as polyester, polyester pellets, bean bag material such as polystyrene beads, air filled compartment, or any material that provides a flexible layer for patient accommodation.

Heat transfer is maximized when the heating element 10 is in conductive thermal contact with the patient. However, in some embodiments, at least one layer of plastic film is interposed between the heating element 10 and the patient to protect the heating element 10. One or more layers of thin plastic film may form an upper shell 40 between the heating element 10 and the patient to introduce minimal thermal resistance to heat flow. In certain embodiments the fabric heating element 10 may be laminated between two layers of thin (such as less than 0.003 inches) plastic film (e.g. urethane or polyvinyl chloride) and may also be stretchy. Laminating a thin layer of plastic film directly onto each side of the heating element 10 protects the heating element fabric from damage by liquids and oxidation. Thin layers of plastic film are sufficient to protect the heating element 10 from liquid and gases, add minimal if any stiffness to the construction, and still allow the heating element 10 to stretch and return to its original shape. This is in contrast to some other conductive fabrics which require lamination between two thick layers of plastic film in order to provide structural strength and durability, resulting in a stiff and non-stretchable heater.

The heating element 10 can stretch in at least one dimension and in some embodiments in two dimensions, such that it can easily deform from a flat planar surface to a half sphere type of formation when loaded with the weight of a patient, particularly of a bony prominence. Since the heat output of the heating element 10 is constant, the heat output per area (Watt density) will decrease as an area of the heating element material is stretched, for example, from a planar shape such as a circle into a three dimensional shape such as a half sphere, by the weight of the patient's body or body part. For example, the area of a circle is Ttr², while the area of a half sphere is 2jtr² and is therefore double. Therefore, the Watt density of the heater may be naturally and automatically reduced by up to approximately half in the load-bearing areas as the heater material stretches from the two dimensional shape such as a circle into a three dimensional shape such as substantially a half sphere. This reduction in Watt density due to the increase in surface area caused by stretching results in an automatic, inherent decrease in temperature of the heating element under the points of increased pressure.

The pressure relief provided by the underbody support is maintained by allowing maximal accommodation (allowing the patient to sink into the support) without the heater creating a "hammocking" force. By allowing maximal accommodation and avoiding hammocking, cutaneous blood flow is maximized at the pressure points which minimizes the risk of pressure ulcers. The pressure needed to collapse capillaries is said to be 32 mm Hg. By allowing maximal accommodation and avoiding hammocking, cutaneous blood flow is generally maximized. By maximizing blood flow, the ability of the skin and tissue to absorb heat from the heating element and transfer it to the rest of the body is also maximized. Further, by allowing the patient to sink into the underbody support (accommodation), the surface area of the heating element 10 in contact with the patient is maximized and thus heat transfer is maximized.

In certain embodiments, the conductive or semi-conductive fabric heating element 10 may be made into a heater assembly 1 by attaching two electrical conductors, or bus bars, along opposing ends of the fabric heating element 10. The bus bars may be attached to the heating element material by sewing with electrically conductive thread. This construction maintains flexibility and durability with repeated flexing. The sewn connection between the bus bar and the heating element fabric may result in a connection that is very robust, flexible and tolerant of extreme flexing and resistant to degradation.

According to some embodiments, the bus bars are coupled to the heater by a stitched coupling, for example, formed with electrically conductive thread such as silver- coated polyester or nylon thread (Marktek Inc., Chesterfield, MO), extending through the conductive fabric material and through the bus bars.

Figure 2 depicts a side view of a heater assembly 1 and a stitched bus bar construction. It includes a heating element 10, a first bus bar 62 at a first end 12 of the heating element 10 and a second bus bar 64 at a second end 14 of the heating element 10. A first insulating member 72 is located between first end 12 and first bus bar 62 and a second insulating member 74 is located between second end 14 and second bus bar 64. Conductive thread 80 connects the heating element 10 to the bus bars 62, 64 through the insulating members 72, 74. In this way, the electrical contact points between the bus bars 62, 64 and the heating element 10 may be solely defined by the conductive thread 80 of the stitched couplings.

Insulating members 72, 74 may be fiberglass material strips having an optional polytetrafluoroethylene (PTFE) coating and a thickness of approximately 0.003 inch, for example. Alternatively, electrically insulating members 72, 74 could be comprised of a polymeric film, a polymeric film reinforced with a fibrous material, a cellulose material, a glass fibrous material, rubber sheeting, polymeric or rubber-coated fabric or woven materials or any other suitable electrically insulating material.

The use of conductive thread stitches 80 of the coupling maintains a stable and constant contact with the bus bar 62, 64 on one side and the heating element 10 on the other side of the insulator 72, 74. Specifically, the stitches can produce a stable contact in the face of any degree of flexion, so that the potential problem of intermittent contact between the bus bar 62, 64 and the heating element 10 (that could arise in embodiments where the bus bar relies upon direct physical contact between the surface of the bus bar with the surface of the heating element) can be avoided.

In some embodiments, the power connection between the power source and the heater is located at a portion of the bus bar 62, 64 that is not touching the fabric heating element 10. For example, in some embodiments, the bus bars 62, 64 extend beyond the end of the heating element 10, such as by about 1 to 2 inches, and the power lead is soldered to the bus bar extension 66 such that it is spaced away from and is not physically touching the heating element 10. Such a location of the solder joint of this power connection may make the connection less susceptible to stress and breaking. Other ways of connecting the power lead to the bus bar extension 66 include, but are not limited to, crimping, weaving, or riveting.

A uniform Watt density output across the surfaces of embodiments of the heating element 10 translates into generally uniform heating of the surfaces, but not necessarily a uniform temperature. At locations of a heating element 10 that are in conductive contact with a mass acting as a heat sink, for example a body, the heat is efficiently drawn away from the heating element and into the body. At those locations where a heating element 10 does not come into conductive contact with the body, for example the peripheral portions, an insulating air gap exists between the body and those portions, so that the heat is not drawn off those portions as rapidly. Therefore, those portions of the heating element 10 not in conductive contact with the body will rise in temperature, since heat is not transferred as efficiently from these non-contacting portions as from those in conductive contact with the body. The non- contacting portions of the heating element will reach a higher equilibrium temperature than that of the contacting portions of the heating element. This new equilibrium temperature will be reached when the radiant and convective heat losses equal the constant heat production of the heating element. Under the laws of thermodynamics it can be understood that as long as there is uniform heat production, even at the higher temperature, the radiant and convective heat transfer from non-contact areas of an underbody support of this construction will result in an equivalent or lower heat flux to the skin than the conductive heat flux at the contacting portions operating at the lower temperature. Even though the temperature at non-contacting portions is higher, the Watt density is uniform and, since the radiant and convective heat transfer is less efficient than conductive heat transfer, the non-contacting portions have an equivalent or lower heat flux to the skin. Therefore, by controlling the contacting portions of the heated underbody support to maintain a safe temperature, for example, via a temperature sensor proximate the heating element 10 in a location where the element will be in conductive contact with the body, the non-contacting portions, for example the lateral portions, will also be operating at a safe (although higher) temperature because of the less efficient radiant and convective heat transfer. The higher temperatures in the non-contacting portions also result in more effective radiant and convective heat transfer compared to a lower temperature. According to some embodiments, the heating element 10 comprises a conductive fabric having a relatively small thermal mass such that when a portion of the heating element 10 that is operating at a first higher temperature is touched, suddenly converting a non-contacting portion into a contacting portion, that portion will cool almost instantly to a second lower operating temperature.

Some embodiments include heated mattresses, mattress overlays, and pads that automatically optimize both the safety and efficacy of the warming in multiple zones across the surface of the mattress, mattress overlay, or pad. The zones are differentiated by whether the mattress or mattress overlay is directly contacting the patient or is substantially not contacting the patient. In general, the central portion of the mattress or mattress overlay will be contacting the patient and the lateral edge portions will predominately not be contacting the patient. Therefore, the central region will transfer heat to the patient conductively and the lateral regions will transfer heat to the patient via radiation and natural convection. The location of the central contact zone is predictable because the patient is anesthetized and therefore, is not spontaneously moving or rolling in bed.

Figure 3 is an aerial view of a heater assembly 1 for use in a heated underbody support. As shown in Figure 3, the heating element 10 has a substantially uniform Watt density across its surface. This may be accomplished with a conductive fabric heater material. The central zone and the adjacent peripheral zones of the heating element 10 are powered by the same controller (not shown). The temperature sensor assembly 110 which inputs to the controller is attached to the heating element 10 in a location which is predicted to be in direct conductive contact with the patient's body when the patient is positioned on the support - the central zone. Once the patient is in position on the support, the area of contact between the patient defines a contact portion while the remaining area is the non-contact portion of the support. The central zone is therefore the portion of the heating element upon which a patient is positioned during normal use and is an estimate of where at least the contact portion is most likely to be. Locating the temperature sensor assembly in the central zone can be used to optimize the safety and efficacy of the warming mattress or mattress overlay. During use, in the central zone 10 where the temperature sensor assembly 110 is attached to the heating element 10, the top surface of the heated underbody support is in contact with the patient for effective conductive heat transfer. For safety reasons, the temperature of the heating element 10 in the conductive zone or contact portion may be controlled to temperatures no greater than between about 38 and about 41°C, for example. In the areas of contact between the patient and the mattress or mattress overlay, the patient's body can act as a heat sink and draw heat from the heating element 10. If the temperature sensor assembly 110 in that region senses the temperature of the support decreasing, it provides an input to the controller, and the controller responds by increasing the electrical power to the entire heating element 10. The temperature of the central zone of the heating element 10 may eventually reach—but not exceed—the set point. This assures optimal heat transfer as well as optimal safety in the contact portion which is the conductive heat transfer region.

In the adjacent peripheral zones, where the heated underbody support is typically substantially not contacting the patient, the added electrical power to the whole heating element 10 results in an increased heating element 10 temperature, which may be greater than the set point or desired temperature as directed by a user. This occurs because there is no heat sink in contact with the heating element 10 to remove the heat. The non- contact portion will be warmer than the contacting portion. The increased temperature in the non-contact portion results in more effective radiant heat transfer in the noncontact portion than if this phenomenon had not occurred. However, since radiant heat transfer is less efficient than conductive heat transfer, despite the higher temperature, the radiant heat is still safe.

For example, the central zone is located substantially in the central area of the support, extending along the longitudinal midline of the support and measuring about 12 inches wide and about 36 inches long. The peripheral zone is in general, the 4-6 inch wide strip of heater running longitudinally along each side edge of the support.

Additionally, the conductive fabric heating elements 10 may have a low thermal mass. Therefore, if the peripheral portion of the heated underbody support that is operating at the higher temperature is touched, suddenly converting a non-contact zone into a contact zone, that part of the heating element 10 quickly cools to the safe operating temperature of the conductive central zone. The non-contact peripheral zones 14 of a heated underbody support may momentarily feel warm when contacted, but will quickly cool to the lower temperature of the contact zone without transferring sufficient thermal energy to injure the patient. Thermal mass, or heat storing capacity, is commonly defined as the product of the mass and the specific heat of a material. Materials with a low specific heat, a low density, or a combination thereof, will exhibit a low thermal mass. For example, a polymer such as polyurethane, with a density of 1 100 kg/m and a specific heat of 1.7 kiloJoules (kJ) per kilogram-degree Kelvin has a volumetric heat capacity of 1870 kJ/ m³-°K, and foam can have a heat capacity of 20-200 kJ/ m³-°K. A thin layer of polyurethane film covering a fabric heating element and a foam layer has significantly lower thermal mass than a water mattress, for example, given the volumetric heat of water of 4180 kJ/ m³-°K. The thermal mass of a heated underbody support can therefore be reduced by using components that exhibit a low density and/or specific heat. In addition, reducing the thickness, or total volume of materials used in the shell, for example, will reduce the thermal mass of the heated underbody support. Various embodiments may be made with materials with a low thermal mass such as films, fabrics and foams. Some embodiments may not incorporate materials such as thick pieces of metal, liquid water or water-based materials such as gels that have relatively high thermal masses.

In these embodiments, when the temperature sensor assembly 1 10 is attached to an area of the heating element 10 that is typically in conductive contact with the patient during normal use, any other area of the heating element 10 that is also in conductive contact with the patient will also be at or near the set point or desired temperature. The temperature differentiation and location of the zones is automatic and depends on whether or not there is conductive contact between the heating element 10 and the patient.

Various embodiments therefore optimize both heat transfer and safety by automatically creating multiple zones in the heated underbody support. The non-contact, radiant heat zones which are typically peripheral, operate at a higher temperature than the patient contact, conductive heat zones which are typically central.

When not stretched, fabric heating elements 10 as described herein provide an even heat output or Watt density across their surface, unless they are folded or wrinkled which can double or triple the heating element 10 layers in the folded or wrinkled portion. The entire heating element 10 may have a relatively low Watt density, such as less than 0.5 watts per square inch, for example. Therefore, some embodiments prevent local wrinkling of the heating element 10. An embodiment of a heated mattress overlay 2 including a heater assembly 1 and a compressible material layer 20 and having reduced wrinkling or folding is shown in Figure 4. It should be noted, however, that whether a unit is described as a heated mattress, heated mattress overlay, or heated pad is largely unimportant, and most embodiments could be used variously as heated underbody supports. While a heated mattress overlay may have a thin layer of padding, a heated pad typically has padding that may be thin or thick, a heated mattress may have an even thicker layer of padding. As such, various embodiments may be used alone, in the manner of a mattress, or on top of a mattress, in the manner of a mattress overlay.

Descriptions relating to heated mattress overlays therefore also apply to descriptions of heated mattresses and heated pads, and vice versa.

The mattress overlay 2 as shown in Figure 4 includes a fabric heating element 10 with bus bars 62, 64 attached that is additionally attached to a layer of foam 20 by a layer of adhesive 30 beneath the heating element 10. To prevent wrinkling, the compressible material layer 20 may be comprised of a simple urethane upholstery foam or its equivalent or one of the many "high tech" foams such as visco-elastic foams. Many foams are suitable for the compressible material layer 20 but should be durable and able to prevent wrinkling of the heater during use, yet should also be flexible, stretchable and accommodating. In the embodiment shown, the mattress overlay 2 also includes an upper shell 40 and a lower shell 42 forming an outer shell that encases the heater assembly 1 and foam layer.

The compressible material layer 20 may be a single layer of foam or may be a stack of materials that includes a layer of foam, for example. This stack could include foam layers of different densities, different accommodation properties, different stiffness or different polymers. Additionally, the compressible material layers can include other materials such as woven or non-woven fabrics or films, to achieve other characteristics such as lateral stiffness or durability and strength. The term compressible material layer 20 therefore refers generally to single layers of compressible material such as foam as well as multilayered stacks that may include one or more layers of foam and may include other materials. Also, the layer of compressible material may alternatively be a layer of foam as described above.

Attachment of the heating element 10 to the compressible material layer 20 may be achieved by adhesive bonding across the entire interface between the two. In alternative embodiments, such as the embodiment shown in Figure 5, the heating element may be bonded to an overlying plastic film layer comprising an upper shell 40. In the embodiment shown, the heated mattress overlay 2 further includes a lower shell 42 beneath the compressible material layer 20.

An alternative embodiment is shown in the heated mattress overlay 2 of Figure 7, a cross section of which is shown in Figure 6. In this embodiment, the fabric heating element 10 is anchored to a shell including an upper shell 40 and a lower shell 42 along its edges 12, 14, 16, 18 and thus held in an extended and wrinkle-free condition.

Anchoring strips 46 comprised of plastic film or a suitable alternative are attached along the edges 12, 14, 16, 18 of the heating element 10, such as by sewing to form a sewn connection 85, though other forms of attachment may be used such as adhesive bonding. The anchoring strips 46 may extend along all four edges 12, 14, 16, 18 of the heating element 10 to form a peripheral bond 48. Alternatively, the anchoring strips 46 may extend along only one pair of opposing edges such as edges 12 and 14 or edges 16 and 18. The anchoring strips 46 may be made of the same material as the shells 40, 42, such as plastic film, and therefore can be bonded around the periphery of the mattress overlay 2, being sandwiched between and incorporated into the bond between the upper shell 40 and lower shell 42.

To maintain flexibility, conformability and stretchability, the upper and/or lower shell 42, 44 may be adhered to the heating element 10 or the compressible material layer 20, across their broad surfaces as shown, for example, in Figure 5, or may not be so adhered. However, in an alternate embodiment the heating element 10 can be bonded to the upper shell 40, for example. This may be advantageous for minimizing wrinkling of the heating element 10 or plastic film layer of the shell 40, 42.

Stretching the heating element 10 from the edges 12, 14 could result in hammocking of the heating element 10, such as if the mattress overlay 2 or pad is anchored tightly to the operating room table along the lateral edges. Various embodiments therefore include a beveled edge 24 on the compressible material layer 20, as shown in Figure 8, for example, to help prevent hammocking by creating a slight excess of heating element 10 material as the heating element 10 transitions across the angle between the upper surface 21 of the compressible material layer 20 and the beveled edges 22,24. Additionally, the angle also creates an area of compressible foam that can compress in response to the heating element 10 being deformed by a weight resulting in the heating element 10 pulling toward the center from the edges 12, 14. Rather than being stretched tight out to the edge as would occur with a non-beveled compressible material layer 20, thereby potentially forming a hammock, the heating element 10 moves toward the center by compressing the compressible material layer 20 at the angle between the upper surface 21 and the beveled edge 24 of the compressible material layer 20, in response to deformation by a weight applied to the central area of the heated mattress or mattress overlay 2. In this way, the risk of hammocking is further reduced or eliminated.

The compressible material layer 20 (or layer of compressible material) supporting the heater assembly 1 could be almost any thickness that is advantageous for the given application (for example, 0.5-6.0 inches). The compressible material layer 20 may be uniform in thickness and density or it may be contoured in thickness, shaped, scored or segmented according to areas of different densities.

Figure 8 depicts a cross section of a heated mattress overlay 2 including a shaped compressible material layer 20 according to various embodiments. In this embodiment, the compressible material layer 20 is beveled or tapered along one or more edges, such as the edges that abut and support the bus bars 62, 64 which are attached to the compressible material layer 20 along the beveled edges 22, 24. The compressible material layer 20 is generally planar with an upper surface 21 and an opposing and parallel lower surface 23. The beveled ends 22, 24 of the compressible material layer 20 are not perpendicular to the surfaces 21, 23 but rather angle inwardly, toward the upper surface 21. On cross section, the compressible material layer 20 is trapezoidal in shape rather than rectangular, with the lower surface 23 forming the larger trapezoid base and the upper surface 21 forming the smaller trapezoid top. Alternatively, the lower portion of the edge could be perpendicular to the bottom surface while only the upper portion of the edge may be angled inwardly to form a bevel. Other embodiments including beveled edges are also anticipated.

The portions of the heating element 10 attached to the bus bars 62, 64 may be bonded to the compressible material layer 20 along the beveled ends 22, 24. Locating the bus bars 62, 64 on the beveled ends 22, 24 of the compressible material layer 20 provides some protection of the bus bars 62, 64 from mechanical stress when patients are sitting or lying on the underbody support. Alternatively, to provide additional protection to the bus bars 62, 64, the heating element 10 may be wrapped around the compressible material layer 20 and onto the bottom surface 23 so that the bus bars 62, 64 are located under the compressible material layer beveled ends 22, 24 and attached to the bottom surface 23 as shown in the cross section shown in Figure 9, for example. In a further alternative shown in Figure 10, the beveled piece of foam that is removed from the compressible material layer 20 or any other triangular or wedge shaped piece of foam of complementary size and shape to fit the space may be bonded over the heater assembly's bus bars 62, 64, along the beveled edges 22, 24 of the compressible material layer 20 to form a filler 25, to fill in the beveled space and protect the bus bars 62, 64. The foam filler 25 may be sized such that, when in place above the bus bars, the horizontal upper surface of the heated mattress overlay 2 (or other underbody support) above the central, non-beveled portion of the foam, is level with the horizontal upper surface of the overlay 2 above the beveled end 24. In these embodiments the heating element 10 extends across the upper surface 21 of the compressible material layer 20, and the bus bars 62, 64 are away from and lower than the upper surface 21. In this way, the bus bars 62, 64 may be physically protected from damage by bonding them onto or beneath the beveled edges 22, 24 of the compressible material layer 20, where they are effectively recessed from the upper surface 21 of the compressible material layer 20. The beveled edges 22, 24 of the compressible material layer 20 allow the bus bars 62, 64 to be optionally covered with a foam filler 25 to act as a protective barrier in this location for added protection, without adversely affecting the look of the smooth top surface of the underbody support, thereby basically filling the bevel space with a foam filler 25 to create an overall rectangular cross sectional shape. In other embodiments, a portion of the compressible material layer 20 is thinned or scored in an area, from one lateral edge to the other of the area, with the area located to overlie the area of transition from one cushion of an operating table to the adjacent cushion under normal conditions of use. The thinning or scoring may be on the bottom surface 23 of the compressible material layer 20 and therefore away from the patient contact top surface 21. Since operating room tables are designed to flex at this area between the operating table cushions, a thinned compressible material layer 20 at the area of transition between cushions will aid in flexion of the heating element 10 and reduce the chances of the heating element 10 wrinkling during flexion. Alternatively, the compressible material layer 20 could be scored or cut or otherwise have one or more gaps or channels completely through or partially through its thickness on the bottom surface 23 at the flexion locations or other areas where added flexibility is important, as shown in Figure 11 , for example. In the embodiment shown, multiple small channels 27 are present in a portion of the compressible material layer 20 where the compressible material layer 20 is thinner. These channels 27 may extend across the compressible material layer 20, from one end to the opposing end, such as across the width or the length of the compressible material layer 20, such as in a direction parallel to and aligned with the transition between operating table cushions. In use, the underbody support may be positioned over a table or bed with which it is designed to be used such that the channels are located over the flexion locations of the table or bed. The table or bed may then be adjusted by bending at a flexion point (such as to raise or lower a patient's upper body or legs by bending or extending the patient at his or her hips) and the compressible material layer 20 of the underbody support can bend easily at this location due to thinness or scoring at the location of flexion, while the heating element 10 can likewise bend without wrinkling or folding due to its flexibility and elasticity.

In some embodiments, the compressible material layer 20 may be thinned or scored or have gaps or channels longitudinally in order to increase flexibility for bending the heated underbody support around a longitudinal axis such as a long axis of a body. This may be advantageous to aid in wrapping the heated underbody support around a patient being in the lateral position while laying within a "bean bag" or "peg board" positioner. The longitudinal thinning or scoring or presence of gaps or channels allows the heated underbody support to be wrapped around the dependent portion of the patient, increasing the area of surface contact between the heating element 10 and the skin while avoiding wrinkling of the heating element 10 due to the bending of the compressible material layer 20. In these embodiments, the bending of the compressible material layer 20 can be facilitated by corrugations in the lower shell 42, which may be created by , at a location corresponding to or adjacent to the location of the gaps or channels in the compressible material layer 20. The corrugations of the shell material may be longitudinal or from side to side. The excess lower shell material created by the corrugations may allow the support to be bent forward at the edges or ends, without causing the upper shell 40 and heating element 10 to wrinkle. The redundant lower shell material 42 of the corrugations, in conjunction with gaps or channels in the compressible material layer 20, allow the lower shell to stretch when the support is bent forward, rather than the upper shell 40 and heater element 10 compressing and wrinkling.

In some embodiments, the compressible material layer 20 is segmented into portions having different thicknesses or different material composition or characteristics. For example, the compressible material layer 20 may include a central portion that may be a rectangular, round or oval section portion within a surrounding portion. Other sectional shapes are anticipated. The surrounding portion may resemble a picture frame or may only surround a portion of the central portion. The central section or sections may be filled with a plug of less dense foam, for example, to increase the accommodation of lightweight pediatric patients or patients' extremities. The surrounding portion of the compressible material layer 20 which may surround the plug may be a denser foam that is more suitable for stabilizing the heating element 10, for example to prevent wrinkling of the heating element 10. An example of such an embodiment is shown in Figure 12, which is an aerial view of a heated mattress overlay 2 with a compressible material layer 20 with a centrally located plug 27 of less dense foam.

In still other embodiments, such as the heated mattress overlay 2 embodiment shown in the cross section in Figure 13 or other heated underbody supports, the compressible material layer 20 includes a depression 29 in a given location to encourage the proper location of the patient on the mattress overlay 2 by contouring the

compressible material layer 20, for example. The depression 29 may also stabilize small pediatric patients on the mattress overlay 2. The depression 29 may be a longitudinal, semicircular half-pipe shape gap or cut out that creates a trough-like depression for the pediatric patient to lay in. A depression 29 in the compressible material layer 20 for small pediatric patients may also increase the amount of skin surface in contact with the heating element 10 by extending the heating element 10 up the sides of the patient's body. The increased surface area of the support contacting the sides of the pediatric patient increases the heat transfer between the support and the patient. The depression 29 also assures accurate positioning so that the patient is contacting the temperature sensor assembly 110 if it is located substantially in the middle or at or near the bottom of the depression 29. For all of these reasons, a pediatric heated mattress or mattress overlay 2 with a longitudinal depression 29 cut into the compressible material layer 20, may be more effective at warming pediatric patients than a simple flat underbody support. Such heated underbody supports may also be more effective for heating adult patients. Other examples of contouring, shaping or segmenting the compressible material layer 20 are anticipated.

In some embodiments, the temperature sensor assembly 1 10 includes a substrate, for example, of polyimide (Kapton), on which the temperature sensor, for example, a surface mount chip thermistor (such as a Panasonic ERT-J1VG103FA: 10K, 1% chip thermistor), is mounted. A heat spreader, for example, a copper or aluminum foil, is mounted to an opposite side of the substrate, for example, being bonded with a pressure- sensitive adhesive. In some embodiments, a secondary over-temperature sensor assembly 115 of similar construction to the temperature sensor assembly 1 10 may be located within one inch of the primary control sensor, so that both the temperature sensor assembly 1 10 and the secondary over-temperature sensor assembly 115 may respond to the same inputs. In some embodiments, both assemblies 110, 115 are mounted to the same heat spreader.

Figure 14 is an aerial view of a heated mattress overlay 2 in which a thin layer (such as less than about 0.5 inches) of compressible material such as foam is located around the temperature sensor assembly 110 and the over- temperature sensors 1 15 to limit the effect of environmental or ambient temperatures in instances where the patient is not properly positioned over the temperature sensor assembly 110. Alternatively, a thin layer of compressible material such as foam may cover some or all of the upper surface of the heater assembly 1. In some alternative embodiments, the material layer may be in the form of a ring 120 surrounding the temperature sensor assembly 110 and the over- temperature sensor assembly 115, as shown in Figure 15. When the patient is not positioned over the temperature sensor assembly 1 10 and the over-temperature sensor assembly 1 15, the ring 120 will remain expanded (uncompressed) and lift the upper shell 40 away from the temperature sensor assembly 110, creating an air space 122 within the ring of foam 120 and between the temperature sensor assembly 110 and the upper shell 40. In this instance, the air space 122 will act as a thermal insulator, minimizing the influence of the environmental temperature on the assemblies 1 10, 115. The space within the ring 120 should be large enough (for example about 0.5 to about 2.0 inches) and the ring material should be compressible enough to allow the over-laying layer of plastic film of the upper shell 40 to be compressed directly against the assemblies 1 10, 115 when a patient is laying on the temperature sensor assembly 110 and the over-temperature sensor assembly 115. In this condition, the temperature sensor assembly 110 and over- temperature sensor assembly 1 15 will respond to the temperature of the heating element 10 that is in direct thermal contact with the patient.

To prevent overheating, certain embodiments include one or more temperature sensor assemblies 110 in the heated underbody support that can sense the temperature in a desired area and then provide feedback to a controller. The temperature sensor assembly 110 can be placed in an area that would be in contact with a patient as described above or in an area that would reflect an average temperature of the heated underbody support. The controller may shut off the power supply to the heating element and/or triggers an alarm, such as an audible or visible alarm, if the sensed temperature is too high, such as if the temperature is at or above a maximum or threshold temperature. Thus, the temperature sensor assembly 110 therefore acts as a safety feature to help protect patients from overheating.

The temperature sensor assembly 1 10 may have a single temperature sensor or multiple temperature sensors. For example, the temperature sensors can be provided in the form of conventional temperature sensors, over-temperature sensors, and super-over temperature sensors, as described in U.S. Application No. 11/537,189, the contents of which are incorporated herein by reference. Each temperature sensor can provide input to the controller. The temperature sensors can all have the same threshold temperature or some can have different threshold temperatures. For example, sensors located in an outer or peripheral area 116 of the heating element 10 that would not normally be in contact with a patient may have a higher threshold temperature than sensors located in an area that would normally be in contact with a patient during normal use.

The combination of conductive fabric heating elements 10 made from flexible and stretchable material, bus bars 62, 64 attached near opposing edges 12, 14 of the heating element 10, one or more temperature sensors 110 and a controller, comprises a heater assembly 1 according to some embodiments. The heater assembly 1 may be secured to a compressible material layer 20 or other compressible layer and may be covered with a water-resistant shell 40, 42 that may be made of a stretchable plastic film such as urethane or PVC, however, other film materials and fiber-reinforced films are anticipated.

The shell 40, 42 protects and isolates the heater assembly 1 from an external environment of the heater assembly 1 or heated underbody support and may further protect a patient disposed on the heated underbody support from electrical shock hazards. According to some embodiments, the shell 40, 42 may be waterproof to prevent fluids, for example, bodily fluids, IV fluids, or cleaning fluids, from contacting the heater assembly 1 , and may further include an anti-microbial element, such as SILVERion™ antimicrobial available from Domestic Fabrics Corporation (Kinston, North Carolina), which is extruded in the plastic film of the shell material.

In some embodiments, a layer of plastic film is placed over each broad surface of the heater assembly 1 , as an upper shell 40 and a lower shell 42 but is not bonded to the heater assembly. The two layers of plastic film are bonded to each other around the periphery of the heater assembly 1 to form a water-resistant shell. The bond may be from heat, radio frequency (RF), ultrasound, solvent or adhesive, for example. The heater assembly 1 may be "free floating" within the shell with no attachment to the shell, or can be attached to the shell, such as only at the edges 12, 14, 16, 18 of the heater assembly 1 as described above, for example. This bond construction around the periphery of the heated underbody support creates a durable shell without folds, creases, crevasses or sewing needle holes that can collect infectious debris and be difficult to clean. The heater assembly 1 covered by a shell of plastic film and optionally including a foam or other support layer comprises a heated mattress, mattress overlay, or pad according to some embodiments.

The heater assembly 1 can be encased in a shell of plastic film as described, or may have no shell. With or without a shell or compressible material layer 20, it can be used as a mattress overlay on top of, or can be inserted into, a pressure reducing mattress. For example, since pressure reducing mattresses typically have water resistant covers, the heater assembly 1 may be inserted directly into the mattress, inside the mattress cover, without a shell on the heater assembly 1. In either case, the heated underbody support is designed to have little or no negative impact on the pressure reducing capabilities of the mattress on which it is laying or into which it is inserted.

In some embodiments, a high tech foam may be included in the compressible material layer 20 or may be in addition to the layer of compressible material 20, to reduce the pressure exerted against the patient's skin during surgery. High tech foams include but are not limited to visco-elastic foams that are designed to maximize accommodation of the patient into the mattress. As previously noted, accommodation refers to the sinking of the user, such as the patient, into the underbody support until a maximal amount of support surface area is in contact with a maximal amount of skin surface, and the pressure exerted across the skin surface is as uniform as possible. These high tech foam materials may accommodate the patient more effectively than simple urethane upholstery foam. Unlike prior art mattress heaters or heating materials, the unique stretchable, flexible, free floating design of the heater assemblies 1 described herein allow them to overlay a layer of visco-elastic foam and maintain the accommodation properties of the foam. Further, the heater assembly 1 may be soft, flexible and stretchable enough to be the separated from the patient by only a single layer of plastic film and still be comfortable. The avoidance of multiple layers of materials interposed between the patient and the mattress foam maximizes accommodation and heat transfer.

In embodiments comprising heated mattresses 3 including foam layers 150, a water-resistant shell or cover 160 may encase the foam 150 as shown, for example, in Figure 25. The foam 150 may be simple urethane foam or high-tech foam such as visco- elastic foam, for example. The cover 160 may be made of plastic film that has been extruded onto a woven fabric (e.g., Naugahyde), for example. In one embodiment, the heater assembly 1 may be located within or may be removably inserted directly into the mattress cover 160, with or without a shell 40 on the heater assembly 1. The heater assembly 1 may be placed directly on top of the mattress foam 150 inside the cover 160 or a heater assembly 1 (with its own shell) may be placed on top of a mattress outside of the mattress cover 160. If a foam mattress has its own shell, the thickness of the shell 40 of the heater assembly 1 can be reduced to, for example, about 0.003 and about 0.010 inch, or even omitted, because the heater assembly 1 is protected from mechanical damage by the cover 160 of the mattress 150. The thinner shell material improves the stretch-ability of the shell. Alternately, the heating element 10 may be bonded directly to the mattress foam 150.

The thermal effectiveness of this heated underbody support can be optimized when the heating element 10 is overlaying a layer that can provide maximal

accommodation of the patient positioned on the support. In this condition, the heating element 10 is in contact with a maximal amount of the patient's skin surface which maximizes heat transfer. Heated underbody supports made with inflatable air chambers forming or included in the compressible material layer 20 or in addition to the compressible material layer 20 can provide excellent accommodation. Further, a heated underbody support with excellent accommodation properties having a heating element 10 as described herein avoids degrading the accommodation properties of the mattress when a heater assembly 1 is added. Therefore, the combination of the heater assembly 1 design with an accommodating mattress such as a mattress made with one or more inflatable air chambers 170 as shown in Figure 17, for example, is advantageous and synergistic for the effectiveness of both technologies.

An embodiment of a heated mattress 3 comprising one or more air chambers 170,

172 and a heater assembly 1 overlaying the one or more air chambers 170, 172 is shown in Figs. 17, 18, and 19. In some embodiments, a single air chamber 170 or a plurality of elongated inflatable chambers 172 are positioned under the heater assembly 1. The plurality of elongated inflatable chambers 172 may be cylindrical in shape and may be oriented in parallel and positioned side -by-side one another, with their long axes extending substantially from one side of the mattress to the other side. However, other inflatable chamber shapes and orientations are anticipated. The inflatable chambers 172 may be round or ovoid in cross section. They may or may not be physically secured to the adjacent air chamber. Alternately, they could be secured to a base sheet or simply positioned and contained within the mattress cover 160 without being secured. The chambers 170, 172 may be made of a fiber-reinforced plastic film or a plastic film that has been bonded, laminated or extruded onto a woven or non-woven fabric reinforcing layer. Urethane may be used as the plastic film, but other plastic film materials are anticipated. Woven nylon may be used as the reinforcing layer, but other fabric materials are anticipated.

The inflatable chamber 170 or chambers 172 can be sealed and static, or connected together in fluid connection to allow redistribution of air between the chambers 172. In some embodiments, the chamber 170 or chambers 172 can be actively inflated and deflated while the heated mattress 3 is in use. The inflatable chambers 172 may be inflated and deflated each independently, all simultaneously, or in separate groups, while the heated mattress 3 is in use. In some embodiments, the chambers 172 are each a part of two separate groups and may be segregated for example by every other chamber 172 (alternating chambers 172) according to their relative side -by-side positions. A conduit or conduits may be in separate independent fluid communication with each chamber 172 of the group of inflatable chambers for independently introducing or removing air from that group of inflatable chambers.

Alternately, there may be only a single group of chambers 172 or there may be more than two groups of chambers 172 which can be separately inflated or deflated. If multiple groups of chambers 172 are used, they may or may not be evenly or

symmetrically arranged. For example, chamber groups may be separated according to the amount of weight-bearing associated with that area. For example, chambers 172 in greater weight bearing areas, such as the torso and hips, may be in a first group, while chambers 172 in areas bearing less weight, such as those supporting the head and legs, may be a separate group of chambers 172. In this way, the lighter portions of the patient's body may be supported by chambers 172 that are inflated to a lower air pressure than chambers 172 that support more weight/heavier body portions. Chambers 172 may be secured to the adjacent chamber or to a base sheet or may be secured by the ends to an element running along each side of the mattress 3, and in some embodiments the chambers 172 and their connectors for fluid connection may be individually detachable. In this instance, if a single chamber 172 or connector fails or is damaged, it can be replaced without requiring the replacement of the entire inflatable heated mattress 3.

The material forming the chamber 170 or chambers 172, such as a plastic film, may be bondable with RF, ultrasound, heat, solvent, or other bonding techniques. The film or film layer of the laminate may be folded back on itself and a single longitudinal and two end bonds may cooperate to form an inflatable chamber 170, 172. More complex chamber construction and bonding embodiments are anticipated.

The conduit fluid connection for air flow to and from and between the inflatable chambers 172 may be plastic tubing, for example. The inlet into the inflatable chamber 172 can be through one of the bonded seams or may be through a surface of the chamber 172. To prevent occlusion of the tubing at the inlet, the tubing may extend one or more inches into the chamber. Other conduits are anticipated, such as a molded or inflatable plenum that may run the length of the heated mattress 3.

In some embodiments, a heater assembly 1 (such as a heater assembly 1 encased within a water resistant shell) is placed on top of the inflatable chambers 170, 172 so that the conductive fabric heating element 10 is at or near the top surface of the heated mattress 3. Alternately, a heater assembly 1 (without a shell) could be placed on top of the inflatable chambers 170, 172 so that the heating element 10 is at or near the top surface of the mattress. The heated mattress 3 may include a flexible, water resistant cover 160 that encases the heater assembly 1 and the inflatable chambers 170, 172.

In some embodiments, the water resistant mattress cover 160 is a plastic film laminated or extruded onto a woven or knit fabric such as "Naugahyde." This construction is soft and durable. Alternately, the cover 160 can be made of plastic film, fiber-reinforced plastic film or a plastic film laminated or bonded to a woven, non- woven, or knit fabric.

The heater assembly 1 of the heated mattress 3 may be "free floating" within the water resistant cover 160 of the heated mattress 3. Alternately, the heater assembly 1 may be attached to the chamber 170 or chambers 172 or foam 150 or attached to the cover 160, either at the edges of the heater assembly 1 or on or across the top or bottom surface of the heating element 10.

The inflatable heated mattress 3 may include pressure sensor assemblies capable of detecting in real time the actual internal air pressure of the inflatable chambers 170, 172 and may also include a comparator which may be in operational communication with the controller for comparing a desired internal air pressure value of the inflatable chambers 170, 172 with the actual internal air pressure, and a pressure adjusting assembly, also in operational communication with the controller, for adjusting the actual internal pressure. The controller may be activated by active feedback data derived from the comparator for maintaining a desired internal pressure value in the inflatable chambers 170, 172 by adjusting the amount of inflation of the inflatable chamber 170 or of the groups of inflatable chambers, such as first and second groups of inflatable chambers 172.

The controller may be operationally connected to a first conduit and a second (or multiple) conduit and a pump for inflating the air chamber 170 or plurality of inflatable chambers 172. Each chamber 172 or plurality of chambers 172 may be independent of each other chamber 172 so that each chamber 172 may react to air pressure changes independently, or may be connected as a group and may react in concert with the air pressure changes in the other chambers 172 of the group. The air may be redistributed within the chambers 172 and the interface pressure may be maintained at any point on the top surface of each of the plurality of chambers 172 which is engaged with an anatomical portion of the user's body, at an average pressure below a capillary occlusion pressure threshold of 32 mm Hg, for example.

The optimal air pressure in the chambers may be predetermined, for example, at a pressure between about 0.4 and about 0.6 psi. The controller may add to or release air from the chambers, in order to maintain a stable and constant pressure in the chambers when the mattress is loaded with a patient. The predetermined pressure may be programmed into the controller or it may be selected by the operator.

Alternately, the controller may include an algorithm for determining the optimal air pressure in the chambers 170, 172, for each patient size, shape, weight and position, to achieve the maximal accommodation of the patient into the air chambers. Maximal accommodation occurs when the chambers 170, 172 are collapsed to a point where a maximal surface area is in contact with the patient and yet the protruding areas such as the patient's butt in the supine position or the hip and shoulder in the lateral position, are not "bottoming out" against the table below or other surface beneath the mattress. If the chambers 170, 172 are inflated more than is needed to support the patient, the patient effectively would be laying on the uppermost part of each over-inflated tubular chamber and is supported by a relatively small surface area. If the chambers 170, 172 are deflated too much, protruding parts of the patient would "bottom out" and be resting on the table or other surface. Both of these conditions result in significant and potentially dangerous pressure being applied to the patient's skin. The optimal air pressure is somewhere in between these two extremes, where the patient in the given position is maximally accommodated into the chamber without "bottoming out," effectively floating.

One way to determine the amount of air pressure that is optimal for maximum accommodation is to inflate the chambers to a pressure that is expected to be greater than the optimal pressure, for example 1.0-1.5psi. Then the air is released slowly, such as in increments, allowing time between each release for equilibration of the air in the chamber 170 or groups of chambers 172 if necessary, and an accurate measurement of the static air pressure in the chambers 170, 172 is then taken. The air release increment may be determined by the duration of time that air is released, for example 2-5 seconds.

Alternately the air release increment may be determined by a measured volume of air released. The air release increment may be determined by a combination of time and pressure used to calculate and standardize the volume of air released with each increment. In some embodiments, the duration of air release lengthens as the air pressure decreases resulting in relatively similar volumes of air being released with each increment.

An algorithm which may be used by the controller to determine optimal air pressure, plots the curve of pressures for each sequential air release. The resulting plot has two phases: a first phase wherein the measured pressures decrease relatively rapidly and a second phase wherein the measured pressures decrease relatively slowly. The part of the curve represented by the first phase has a steeper downward slope and the part of the curve represented by the second phase has a more gradual downward slope. The first phase generally represents the over-inflated chambers with the patient supported by a relatively small upper surface area of the chamber. The second phase generally represents the patient sinking into the gradually collapsing chambers, wherein little additional surface area is enlisted with each additional incremental deflation. In the second phase, the patient is effectively "floating" to the maximal extent of the mattresses ability to accommodate the patient.

The controller can identify the pressure at which the pressure change transitions from the steep downward slope of the first phase, to the gradual downward slope of the second phase. The second phase may be identified by identifying a decreased or minimal pressure drop between two sequential air releases. For example, if a decrease of less than about 10% is detected between two sequential air releases, the controller may then stop the air releases and maintain that pressure as the optimal pressure. Depending on the design and sizes of the chambers and the amount of air released in each increment, the pressure drop indicating that the pressure is at the optional pressure may be less than from about 2 to 15% between increments, and may be identified by the air pressure drop between increments being significantly less than the air pressure drop in the first phase. When the second phase is first identified by recording a reduced or minimal pressure drop between sequential air release increments, the air pressure is near the optimal pressure and the controller may be programmed to maintain that air pressure.

Alternately, when the first minimal difference in air pressures are detected with a subsequent air release, the controller may be programmed to release an additional predetermined amount of air or to re-inflate the air chamber with a predetermined amount of air.

A controller which may be used in various embodiments is shown in Figure 29. The controller 182 may be included in a console 180. A shut-off timer 184 and a power supply 186 may each be operatively coupled to the controller 182, meaning that the shut- off timer 184 can be a separate component, or the shut-of timer 184 and the controller 182 can have any other suitable functional relationship. The temperature sensor assembly 110 and over-temperature sensor assembly 115 can be configured to provide temperature information to the controller 182, which may act as a temperature controller. The controller may function to interrupt such power supply (e.g., in an over-temperature condition) or to modify the duty cycle to control the heating element 10 temperature. In embodiments including an inflatable support, an air pressure comparator (not shown) may be in operatively coupled to the controller 182, meaning, like the shut-off timer 184, the air pressure controller can be a separate component, or the air pressure controller and the controller 182 can have any other suitable functional relationship. The air pressure sensor assemblies can be configured to provide air pressure information to the controller 182, which may act as an air pressure controller.

In embodiments comprising heated mattresses 3 including foam layers 150, a water-resistant shell or cover 160 may encase the foam 150 as shown, for example, in Figure 16. The foam 150 may be simple urethane foam or high-tech foam such as visco- elastic foam, for example. The cover 160 may be made of plastic film that has been extruded onto a woven fabric (e.g., Naugahyde), for example. In one embodiment, the heater assembly 1 may be located within or may be removably inserted directly into the mattress cover 160, with or without a shell 40 on the heater assembly 1. The heater assembly 1 may be placed directly on top of the mattress foam 150 inside the cover 160 or a heater assembly 1 (with its own shell) may be placed on top of a mattress outside of the mattress cover 160. If a foam mattress has its own shell, the thickness of the shell 40 of the heater assembly 1 can be reduced to, for example, about 0.003 and about 0.010 inch, or even omitted, because the heater assembly 1 is protected from mechanical damage by the cover 160 of the mattress 150. The thinner shell material improves the stretch-ability of the shell. Alternately, the heating element 10 may be bonded directly to the mattress foam 150.

In the foregoing detailed description, the invention has been described with reference to specific embodiments. However, it may be appreciated that various modifications and changes can be made without departing from the scope of the invention as set forth in the appended claims.

Claims

What is claimed is:

1. A heated underbody support comprising a heated mattress, heated mattress

overlay or heated pad, the heated underbody support comprising:

a heater assembly having an upper surface upon which a user directly or indirectly lays when the heated underbody support is in use, the heater assembly comprising: a flexible heating element comprising a sheet of conductive fabric having a top surface, a bottom surface, a first edge and an opposing second edge, a length, and a width wherein the heating element has a substantially uniform Watt density;

a first bus bar extending along the first edge of the heating element, the first bus bar adapted to receive a supply of electrical power;

a second bus bar extending along the second edge of the heating element;

a temperature sensor;

a layer of compressible material adapted to conform to the user's body when under pressure from the user resting upon the support;

wherein when the user lays upon the upper surface of the support, the area of contact between the user and the upper surface of the support defines a contact portion of the support separate from a non-contact portion of the support,

wherein the temperature sensor is located within the contact portion of the support, and wherein the heating element is adapted to adjust such that a temperature of the contact portion is less than a temperature of the non-contact portion of the support.

2. The heated underbody support of claim 1 further comprising a controller, wherein the controller is adapted to regulate the supply of electrical power to the first bus bar depending upon input from the temperature sensor to maintain a desired temperature.

3. The heated underbody support of claim 2 wherein, when in use with the user positioned on the contact portion and on the temperature sensor, the controller maintains the temperature of the contact portion at the desired temperature which is less than the temperature of the noncontact portion.

4. The heated underbody support of claim 1 wherein the sheet of conductive fabric comprises a fabric coated with an electrically conductive or semi-conductive material.

5. The heated underbody support of claim 4 wherein the conductive or semi- conductive material comprises a carbon fiber or metal containing polymer or ink.

6. The heated underbody support of claims 4 or 5 wherein the sheet of conductive fabric comprises threads separately and individually coated with the conductive or semi- conductive material and wherein the coated threads of the fabric are able to slide relative to each other such that the heating element is stretchable.

7. The heated underbody support of claim 6 wherein the conductive or semi- conductive material comprises a polymer.

8. The heated underbody support of claim 7 wherein the conductive or semi- conductive material comprises polypyrrole.

9. The heated underbody support of claims 1-8 wherein the layer of compressible material comprise a layer of foam having a top surface and a bottom surface, wherein the heating element is located on the top surface of the layer of foam.

10. The heated underbody support of claim 9 wherein the foam layer is contoured such that either the top surface and/or the bottom surface is not planar over the entire surface or the first and second edges of the foam layer are angled inwardly toward the top surface.

11. The heated underbody support of claim 10 wherein the bottom surface of the layer of foam is nonplanar and comprises one or more channels extending substantially across the entire length or width of the layer of foam.

12. The heated underbody support of claim 11 wherein the channel or channels are located at a position that aligns with a line of flexion of a table or mattress with which the underbody support is designed to be used.

13. The heated underbody support of claim 11 wherein the channel or channels are located at a position that aligns with a longitudinal line of flexion allowing the support to flex around a longitudinal axis of the user when the user is laying on the heated underbody support in a lateral position.

14. The heated underbody support of claim 9 wherein the foam layer comprises a central area having a reduced thickness relative to a thickness of a peripheral area of the foam layer.

15. The heated underbody support of claim 9 wherein the top surface of the foam layer comprises a half-cylinder shaped depression in a central area to accommodate, partially surround and accurately position a pediatric patient.

16. The heated underbody support of claim 9 wherein the foam layer comprises a central area and a peripheral area, and wherein the foam material of the central area is less dense than the foam of the peripheral area.

17. The heated underbody support of claims 1-16 further comprising a water resistant shell encasing the heater assembly and the layer of compressible material, the water resistant shell comprising an upper shell and a lower shell which are sealed together along their edges to form a bonded edge of the water resistant shell.

18. The heated underbody support of claim 1-17 wherein the first and second conductive bus bars are attached to the heating element by sewing through the bus bar and the heating element with electrically conductive thread.

19. The heated underbody support of claim 18 wherein a strip of electrically insulating fabric or film is interposed between the heating element and the bus bar, and wherein the bus bar is electrically connected to the heating element by sewing through the bus bar and the electrically insulating fabric or film and the heating element with electrically conductive thread.

20. The heated underbody support of claim 1 wherein the temperature sensor is located in contact with the heating element.

21. The heated underbody support of claim 20 wherein a thin layer of foam is positioned over the temperature sensor on the top surface of the heating element.

22. The heated underbody support of claim 20 wherein a thin ring of foam is positioned around the temperature sensor on the top surface of the heating element.

23. The heated underbody support of claims 1 - 22 wherein the compressible material comprises a flexible air filled chamber.

24. The heated underbody support of claim 23 further comprising one or more additional flexible air filled chambers, wherein the flexible air filled chambers are elongated and have a longitudinal axis, and wherein the flexible air filled chambers are positioned with their longitudinal axis parallel to each other, along side one another, and extending substantially from a first side of the heated underbody support to an opposing second side if the heated underbody support.

25. The heated underbody support of claim 23 further comprising one or more additional flexible air filled chambers, wherein each of the flexible air filled chambers can be inflated and deflated independently while the heated underbody support is in use.

26. The heated underbody support of claim 23 further comprising one or more additional flexible air filled chambers, wherein the flexible air filled chambers can all be inflated and deflated simultaneously while the heated underbody support is in use.

27. The heated underbody support of claim 23 further comprising one or more additional flexible air filled chambers, wherein the flexible air filled chambers can be inflated and deflated in groups while the heated underbody support is in use, wherein the groups comprise less than all of the flexible air filled chambers.

28. The heated underbody support of claim 25 wherein the flexible air filled chambers are elongated and positioned side by side and are in alternating groups such that each flexible air filled chamber is in a different group from each flexible air filled chamber which is beside it.

29. The heated underbody support of claims 23-26 further comprising air conduits, wherein one air conduit is in independent fluid communication with each group of flexible air filled chambers for independently introducing or removing air from that group of flexible air filled chambers.

30. The heated underbody support of claim 29 further comprising a pressure sensor adapted to detect an actual internal air pressure of the flexible air filled chambers, and a controller comprising a comparator for comparing a desired internal air pressure of the flexible air chambers with the actual internal air pressure, the controller further comprising a pressure compensator for adjusting the actual internal pressure, wherein the controller in operative connection with the air conduits and an air pump, and wherein the controller is adapted to adjust the inflation of the groups of flexible air chambers to maintain the desired internal air pressure of the flexible air filled chambers using data derived from the comparator.

31. The heated underbody support of claim 29 wherein each flexible air filled chamber of each group of chambers is in fluid connection with every other flexible air filled chamber of its group so that each flexible air filled chamber reacts to air pressure changes in every other flexible air filled chamber of its group, thereby redistributing changes in air pressure within each flexible air filled chamber of each group, wherein an interface pressure is maintained on a top surface of each of the group of flexible air filled chambers which is in contact with a portion of the user's body at an average pressure below a capillary occlusion pressure threshold of 32 mm Hg.

32. The heated underbody support of claims 1-31 wherein the heating element has a planar shape, wherein in response to pressure the heating element is adapted to stretch into a 3-dimensional compound curve without wrinkling or folding while maintain electrical conductivity, and wherein the heating element is adapted to return to the planar shape when pressure is removed.

33. The heated underbody support of claim 32 wherein the heating element has a first Watt density when in a planar shape and a second Watt density when stretched into a 3 dimensional compound curve, and wherein the first Watt density is greater than the second Watt density.

34. A heated underbody support comprising a heated mattress, heated mattress

overlay or heated pad, the heated underbody support comprising:

a heater assembly comprising:

an upper surface upon which a user directly or indirectly lays when the support is in use;

a flexible heating element comprising a sheet of conductive fabric having a top surface, a bottom surface, a first edge and an opposing second edge, a length, and a width;

a temperature sensor; and

a controller that regulates a supply of power to the flexible heating element

depending upon input from the temperature sensor to maintain a desired temperature; wherein the flexible heating element has a planar shape and an approximately uniform Watt density; and

wherein when the user contacts a portion of the heating element, the heating element is adapted to automatically decrease in temperature in the portion.

35. The heated underbody support of claim 34 wherein when the user lays upon a portion of the upper surface of the support, the area of contact between the person and the support defines a contact portion of the support separate from a non-contact portion of the support, and the heating element is adapted to adjust a temperature of the contact portion to be less than a temperature of the non-contact portion.

36. The heated underbody support of claim 35 wherein the temperature sensor is centrally located on the heating element at a location upon which the user is typically positioned during normal use.

37. The heated underbody support of claim 36 wherein, when in use with the user on the contact portion, the controller maintains the temperature in the contact portion at the desired temperature which is less than the temperature of the non-contact portion.

38. A method of warming a person comprising:

positioning the person on an upper surface of a heated underbody support comprising a heated mattress, heated mattress overlay, or heated pad, the heated underbody support comprising:

a heater assembly comprising:

an upper surface upon which the person is position;

at least one temperature sensor located near the heating element; and

a controller that regulates a supply of power to the heating element depending upon input from the temperature sensor to maintain a desired temperature; activating the underbody support to supply power to the heating element; and

directing the underbody support to maintain a desired temperature,

wherein a location of the person on the support defines a contact portion of the support separate from a non-contact portion of the support, and

wherein a temperature of the contact portion is less than a temperature of the non-contact portion.

39. The method of claim 38 wherein the temperature sensor is centrally located on the heating element and wherein positioning the person comprises positioning the person to be in contact with the temperature sensor or with a portion of the support which overlies the temperature sensor.

40. The method of claim 38 further comprising repositioning the person on the upper surface of the support such that part of the non-contact portion becomes an additional part of the contact portion of the support, wherein a temperature of the additional part of the contact portion automatically reduces to the desired temperature.